Multi-layer sealing film for high seal yield

ABSTRACT

A multi-layer sealing film for high seal yield is provided. In some embodiments, a substrate comprises a vent opening extending through the substrate, from an upper side of the substrate to a lower side of the substrate. The upper side of the substrate has a first pressure, and the lower side of the substrate has a second pressure different than the first pressure. The multi-layer sealing film covers and seals the vent opening to prevent the first pressure from equalizing with the second pressure through the vent opening. Further, the multi-layer sealing film comprises a pair of metal layers and a barrier layer sandwiched between metal layers. Also provided is a microelectromechanical systems (MEMS) package comprising the multilayer sealing film, and a method for manufacturing the multi-layer sealing film.

REFERENCE TO RELATED APPLICATIONS

This Application is a Divisional of U.S. application Ser. No.15/694,176, filed on Sep. 1, 2017, which claims the benefit of U.S.Provisional Application No. 62/427,185, filed on Nov. 29, 2016. Thecontents of the above-referenced Patent Applications are herebyincorporated by reference in their entirety.

BACKGROUND

Microelectromechanical systems (MEMS) devices are microscopic devicesthat integrate mechanical and electrical components to sense physicalquantities and/or to act upon surrounding environments. In recent years,MEMS devices have become increasingly common. For example, MEMSaccelerometers are commonly found in airbag deployment systems, tabletcomputers, and smart phones.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A and 1B illustrate cross-sectional views of various embodimentsof a semiconductor structure with a multi-layer sealing film.

FIGS. 2A and 2B illustrate top views of various embodiments of thesemiconductor structure of FIGS. 1A and 1B.

FIG. 3 illustrates an enlarged cross-sectional view of some embodimentsof a seam in the multi-layer sealing film of FIGS. 1A and 1B.

FIGS. 4A-4C illustrate various views of some embodiments of a MEMSpackage with a multi-layer sealing film.

FIG. 5 illustrates a cross-sectional view of some more detailedembodiments of the MEMS package of FIGS. 4A-4C.

FIGS. 6A-6C illustrate various views of some more detailed embodimentsof the MEMS package of FIG. 5.

FIGS. 7-11, 12A, 12B, 13A, and 13B illustrate a series ofcross-sectional views of some embodiments of a method for manufacturinga MEMS package with a multi-layer sealing film.

FIG. 14 illustrates a flowchart of some embodiments of the method ofFIGS. 7-11, 12A, 12B, 13A, and 13B.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Microelectromechanical systems (MEMS) devices are increasingly packagedwith and electrically coupled to complementary metal-oxide-semiconductor(CMOS) devices. For example, MEMS pressure sensors are increasinglyintegrated with CMOS devices for use in wearable devices, such as smartwatches. A MEMS pressure sensor includes a flexible membrane over acavity hermetically sealed with a reference pressure. Assuming thereference pressure is steady, the flexible membrane deflects inproportion to a difference between an environmental pressure and thereference pressure.

A method for integrating a MEMS pressure sensor with CMOS devicescomprises forming an interconnect structure covering a first substratethat supports CMOS devices. The interconnect structure comprises aplurality of wires, a plurality of vias, and a interconnect dielectriclayer within which the wires and the vias are alternatingly stacked. Afirst etch is performed into the interconnect dielectric layer to form acavity over the first substrate and the CMOS devices, and a secondsubstrate is fusion bonded to the first substrate through theinterconnect dielectric layer. The fusion bonding is limited tohermetically sealing the cavity with a high reference pressure (e.g.,500 millibars or greater), which may be unsuitable for certainapplications. Therefore, to hermetically seal the cavity with a lowreference pressure (e.g., 10 millibars or less), a second etch isperformed through the second substrate to form a vent opening that opensthe cavity. Further, a single, ultra-thick-metal (UTM) layer isdeposited at the low reference pressure to cover and seal the ventopening.

A challenge with sealing the vent opening with the single, UTM layer isthat a seam has a high likelihood of forming along metal grainboundaries of the UTM layer. The seam allows air to pass through thesingle, UTM layer to the cavity, which increases the reference pressureof the cavity beyond allowable limits and leads to failure of the seal.This, in turn, reduces yields during bulk manufacture and increasescosts.

In view of the foregoing, various embodiments of the present applicationare directed towards a multi-layer sealing film for high seal yield. Insome embodiments, a MEMS package comprises a first substrate supportingsemiconductor devices. A interconnect structure covers the firstsubstrate and the semiconductor devices. The interconnect structurecomprises a dielectric layer, and the dielectric layer comprises acavity that is hermetically sealed. A second substrate covers thecavity. The second substrate comprises a vent opening extending throughthe second substrate, from an upper side of the second substrate to thecavity. A multi-layer sealing film covers the vent opening, and furtherseals the vent opening and the cavity. The multi-layer sealing filmcomprises a first metal layer and a second metal layer over the firstmetal layer, and further comprises a barrier layer between the first andsecond metal layers.

Advantageously, the barrier layer stops or limits a seam along grainboundaries of the first metal layer from extending through an entirethickness of the multi-layer sealing film. For example, the barrierlayer may be a metal or ceramic material having smaller grains (orcrystallites) than the metal layers. The smaller grains, in turn,increases the density of grains in the barrier layer and decreases thesize of boundaries between the grains. This causes the grain boundaries(e.g., the whole metal grain boundary) to become discontinuous, therebystopping or limiting the seam at the barrier layer, and preventing airor other gases from passing through the multi-layer sealing film to thecavity. Therefore, the cavity may be sealed with and maintain a lowreference pressure (e.g., about 10 millibars or less), yields may behigh (e.g., greater than 99%) during bulk manufacture, and costs may below. Even more, the first and second metal layers may have a smallthickness, thereby leading to low material costs.

With reference to FIG. 1A, a cross-sectional view 100A of someembodiments of a semiconductor structure with a multi-layer sealing film102 is provided. As illustrated, the multi-layer sealing film 102 isover a substrate 104, on an upper side 104 u of the substrate 104. Thesubstrate 104 may be, for example, a bulk semiconductor substrate, suchas bulk substrate of monocrystalline or polycrystalline silicon, or someother type of substrate. Further, the multi-layer sealing film 102covers and seals a vent opening 106 defined by the substrate 104.

The vent opening 106 extends from the upper side 104 u of the substrate104, through the substrate 104, to a lower side 1041 of the substrate104 that is opposite the upper side 104 u. The upper side 104 u of thesubstrate 104 has a first pressure P₁, and the lower side 1041 of thesubstrate 104 has a second pressure P₂ that is different than the firstpressure P₁. For example, the first pressure P₁ may be greater than thesecond pressure P₂, or vice versa. By sealing the vent opening 106, themulti-layer sealing film 102 advantageously prevents the first pressureP₁ from equalizing with the second pressure P₂ through the vent opening106.

In some embodiments, a minimum dimension D of the vent opening 106 isless than about two times a thickness T of the multi-layer sealing film102 so the multi-layer sealing film 102 does not collapse into the ventopening 106. The minimum dimension D may be, for example, between about0.1-2.0 micrometers, about 0.05-3.5 micrometers, or about 0.5-1.5micrometers. The thickness T may be, for example, between about 2.5-3.5micrometers, about 3.0-3.3 micrometers, or about 1.5-4.0 micrometers.

The multi-layer sealing film 102 comprises a first metal layer 108 a, afirst barrier layer 110 a, a second metal layer 108 b, a second barrierlayer 110 b, and a third metal layer 108 c. The first metal layer 108 ais over and, in some embodiments, contacts the substrate 104. The firstbarrier layer 110 a is over and, in some embodiments, contacts the firstmetal layer 108 a. The second metal layer 108 b is over and, in someembodiments, contacts the first barrier layer 110 a. The second barrierlayer 110 b is over and, in some embodiments, contacts the second metallayer 108 b. The third metal layer 108 c is over and, in someembodiments, contacts the second barrier layer 110 b. In someembodiments, the first, second, and third metal layers 108 a-108 c andthe first and second barrier layers 110 a, 110 b have the same layout.

The first, second, and third metal layers 108 a-108 c are metals withgrain sizes larger than those of the first and second barrier layers 110a, 110 b, and the first and second barrier layers 110 a, 110 b aremetals or ceramics that have grain sizes smaller than those of thefirst, second, and third metal layers 108 a-108 c. For example, thefirst, second, and third metal layers 108 a-108 c may be aluminumcopper, copper, or some other metal, and the first and second barrierlayers 110 a, 110 b may be titanium nitride, titanium tungsten, tungstennitride, tantalum nitride, or some other metal material.

After the multi-layer sealing film 102 is formed, a seam 112 may form atthe vent opening 106, along grain boundaries of the first metal layer108 a. The first and second barrier layers 110 a, 110 b advantageouslystop or limit the seam 112 from extending completely through thethickness T of the multi-layer sealing film 102, along grain boundariesof the first, second, and third metal layers 108 a-108 c. By stopping orlimiting the seam 112, the multi-layer sealing film 102 advantageouslyprevents or limits the likelihood of the first pressure P₁ equalizingwith the second pressure P₂ through the vent opening 106. Accordingly,yield may be high during bulk manufacture of the semiconductorstructure, and the reliability of the multi-layer sealing film 102 maybe high. Further, by stopping or limiting the seam 112, the thickness Tof the multi-layer sealing film 102 may advantageously be small.

In some embodiments, the first, second, and third metal layers 108 a-108c are the same material. In other embodiments, the first, second, andthird metal layers 108 a-108 c are different materials. In yet otherembodiments, some of the first, second, and third metal layers 108 a-108c are the same material and some of the first, second, and third metallayers 108 a-108 c are different materials. For example, the first andsecond metal layers 108 a, 108 b may be aluminum copper, and the thirdmetal layer 108 c may be elemental copper. Further, in some embodiments,the first, second, and third metal layers 108 a-108 c are pure metals ormetal alloys limited to elemental metals. For example, the first,second, and third metal layers 108 a-108 c may be elemental copper,elemental aluminum, aluminum copper, or a combination of the foregoing.

In some embodiments, individual thicknesses T_(m) of the first, second,and third metal layers 108 a-108 c are the same. In other embodiments,the individual thicknesses T_(m) of the first, second, and third metallayers 108 a-108 c are different. In yet other embodiments, some of theindividual thicknesses T_(m) of the first, second, and third metallayers 108 a-108 c are the same and some of the individual thicknessesT_(m) of the first, second, and third metal layers 108 a-108 c aredifferent. For example, the first and third metal layers 108 a, 108 cmay have the same thickness, and the second metal layer 108 b may have adifferent thickness. Further, in some embodiments, the individualthicknesses T_(m) of the first, second, and third metal layers 108 a-108c are each between about 0.75-1.25 micrometers, about 1.0-2.0micrometers, about 0.5-3.0 micrometers, or about 1.25-1.75 micrometers.For example, the individual thicknesses T_(m) of the first, second, andthird metal layers 108 a-108 c may each be about 1 micrometer.

In some embodiments, the first and second barrier layers 110 a, 110 bare conductive and block the diffusion of material from the first,second, and third metal layers 108 a-108 c through the first and secondbarrier layers 110 a, 110 b. For example, where the first, second, andthird metal layers 108 a-108 c include copper, the first and secondbarrier layers 110 a, 110 b may block the diffusion of copper throughthe first and second barrier layers 110 a, 110 b. In some embodiments,the first and second barrier layers 110 a, 110 b are the same material.In other embodiments, the first and second barrier layers 110 a, 110 bare different materials.

In some embodiments, individual thicknesses T_(b) of the first andsecond barrier layers 110 a, 110 b are the same. In other embodiments,the individual thicknesses T_(b) of the first and second barrier layers110 a, 110 b are different. Further, in some embodiments, the individualthicknesses T_(b) of the first and second barrier layers 110 a, 110 bare each between about 500-2000 angstroms, about 1100-1500 angstroms, orabout 1250-1750 angstroms. Further yet, in some embodiments, theindividual thicknesses T_(b) of the first and second barrier layers 110a, 110 b are each less than the individual thicknesses T_(m) of thefirst, second, and third metal layers 108 a-108 c. For example, wherethe individual thicknesses T_(m) of the first, second, and third metallayers 108 a-108 c are about 1 or 1.5 micrometers, the individualthicknesses T_(b) of the first and second barrier layers 110 a, 110 bmay be about 1500 angstroms.

With reference to FIG. 1B, a cross-sectional view 100B of some otherembodiments of the semiconductor structure of FIG. 1A is provided. Asillustrated, the second barrier layer 110 b of FIG. 1A and the thirdmetal layer 108 c of FIG. 1A are omitted. In some embodiments, thethickness T of the multi-layer sealing film 102 is between about 2.5-3.5micrometers, about 3.0-3.3 micrometers, or about 1.5-4.0 micrometers.Further, in some embodiments, the individual thickness T_(b) of thefirst barrier layer 110 a is about 1100-2000 angstroms, about 1250-1750angstroms, or 1500-1700 angstroms, and/or the individual thicknessesT_(m) of the first and second metal layers 108 a, 108 b are each about1.0-2.0 micrometers, about 1.25-1.75 micrometers, or about 1.6-1.7micrometers. For example, the individual thickness T_(b) of the firstbarrier layer 110 a may be about 1500 angstroms, and the individualthicknesses T_(m) of the first and second metal layers 108 a, 108 b maybe about 1.5 micrometers.

While FIGS. 1A and 1B illustrate the multi-layer sealing film 102respectively with two and three metal layers, and respectively with oneand two barrier layers, the multi-layer sealing film 102 may have fouror more metal layers and three or more barrier layers in otherembodiments. In such embodiments, the four or more metal layers and thethree or more barrier layers are alternatingly stacked with the samealternating pattern shown in FIGS. 1A and 1B.

With reference to FIGS. 2A and 2B, top views 200A, 200B of variousembodiments of the semiconductor structure of FIGS. 1A and 1B areprovided. The top views 200A, 200B may, for example, be taken along lineA-A′ in FIG. 1A or FIG. 1B. As illustrated by the top view 200A of FIG.2A, the vent opening 106 is circular, and the minimum dimension D of thevent opening 106 is a diameter of the vent opening 106. Further, themulti-layer sealing film 102 (shown in phantom) completely covers thevent opening 106. As illustrated by the top view 200B of FIG. 2B, thevent opening 106 is laterally elongated, and the minimum dimension D ofthe vent opening 106 is orthogonal to a length L of the vent opening106. Further, as in FIG. 2A, the multi-layer sealing film 102 (shown inphantom) completely covers the vent opening 106.

With reference to FIG. 3, an enlarged cross-sectional view 300 of someembodiments of the seam 112 in the multi-layer sealing film 102 of FIGS.1A and 1B is provided. As illustrated, the first metal layer 108 acomprises metal grains 302. For ease of illustration, only some of themetal grains 302 are labeled 302. Further, the seam 112 extends throughthe first metal layer 108 a, along boundaries of the metal grains 302.

With reference to FIG. 4A, a cross-sectional view 400A of someembodiments of a MEMS package comprising a pair of multi-layer sealingfilms 102 is provided. As illustrated, a support structure 402 underliesand is bonded to a MEMS substrate 404. In some embodiments, the supportstructure 402 is bonded to the MEMS substrate 404 at a bond interface406 between a top surface of the support structure 402 and a bottomsurface of the MEMS substrate 404. The bond interface 406 may be, forexample, planar. In some embodiments, the support structure 402 is abulk semiconductor substrate or an integrated circuit (IC).

The MEMS substrate 404 overlies the support structure 402 and comprisesa MEMS device 408. The MEMS substrate 404 may be or comprise, forexample, monocrystalline silicon, polycrystalline silicon, amorphoussilicon, aluminum copper, oxide, silicon nitride, a piezoelectricmaterial, some other material, or a combination of the foregoing. Insome embodiments, the MEMS substrate 404 is a bulk substrate ofmonocrystalline silicon. In other embodiments, the MEMS substrate 404 isor otherwise comprises a piezoelectric layer, such as, for example, leadzirconate titanate (PZT) or aluminum nitride (AlN). The MEMS device 408is spaced over the support structure 402 by a cavity 410 between theMEMS substrate 404 and the support structure 402, and may be, forexample, a pressure sensor. The cavity 410 is hermetically sealed with areference pressure P_(r) and is recessed into the support structure 402.The reference pressure P_(r) may be, for example, less than about 0.01,0.1, 1, 10, 100, 250, or 500 millibars, and/or may be, for example,between about 0.001-10.000 millibars, about 0.001-1.000 millibars, about0.01-1 millibars, or about 1-10 millibars.

In operation, the MEMS device 408 moves within the cavity 410 inproportion to a pressure difference between the reference pressure P_(r)and an ambient pressure P_(a) of the MEMS package. Further, since thereference pressure P_(r) is fixed, the MEMS device 408 moves within thecavity 410 in proportion to the ambient pressure P_(a). Therefore, themovement of the MEMS device 408 may be measured to sense the ambientpressure P_(a). In some embodiments, the movement of the MEMS device 408is measured using capacitive coupling between the MEMS device 408 and afixed electrode (not shown) neighboring the MEMS device 408. In otherembodiments where the MEMS substrate 404 is or otherwise comprises apiezoelectric layer, the movement of the MEMS device 408 is measuredusing the Piezoelectric Effect.

The MEMS substrate 404 further comprises a pair of vent openings 106.The vent openings 106 are on opposite sides of the cavity 410 and extendfrom the upper side 404 u of the MEMS substrate 404, through the MEMSsubstrate 404, to the cavity 410. In some embodiments, the vent openings106 are each as described in FIG. 1A or 1B and/or in FIG. 2A or 2B. Insome embodiments, the vent openings 106 define the only paths by whichthe reference and ambient pressures P_(r), P_(a) may equalize.

In some embodiments, the cavity 410 comprises a pair of channels 410 c.The channels 410 c are on the opposite sides of the cavity 410 andrespectively underlie the vent openings 106. Further, in someembodiments, the channels 410 c overlie a pair of channel pads 412 c.The channels 410 c are regions of the cavity 410 that have a channeldepth D_(c) less than a bulk depth D_(b) of the cavity 410, and thatfurther have a channel width less than a bulk width of the cavity 410.The channel and bulk widths extend into and out of the cross-sectionalview 400A of FIG. 4A, whereby the channel and bulk widths are notvisible in the cross-sectional view 400A of FIG. 4A. However, examplesof the channel and bulk widths are illustrated in the top view 400B ofFIG. 4B. The channel pads 412 c respectively underlie the channels 410 cand may be, for example, aluminum copper, copper, aluminum, or someother metal.

The multi-layer sealing films 102 are over the MEMS substrate 404, andrespectively cover the vent openings 106 to seal the vent openings 106and the cavity 410. By sealing the vent openings 106 and the cavity 410,the multi-layer sealing films 102 advantageously prevent the ambientpressure P_(a) from equalizing with the reference pressure P_(r) throughthe vent openings 106. The multi-layer sealing films 102 are each asdescribed in FIG. 1A or 1B. Further, the multi-layer sealing films 102each comprise a plurality of metal layers 108 and one or more barrierlayers 110. For ease of illustration, only some of the metal layers 108are labeled 108, and only some of the barrier layers 110 are labeled110.

The metal layers 108 and the barrier layer(s) 110 are alternatinglystacked, examples of which are shown in FIGS. 1A and 1B. Further, themetal layers 108 are metals with grain sizes larger than those of thebarrier layer(s) 110, and the barrier layer(s) 110 are metals orceramics that have grain sizes smaller than those of the metal layers108. For example, the metal layers 108 may be aluminum copper, copper,aluminum, or some other metal, and the the barrier layer(s) 110 may betitanium nitride, titanium tungsten, tungsten nitride, tantalum nitride,or some other barrier material.

After the multi-layer sealing films 102 are formed, seams 112 may format the vent openings 106. The barrier layer(s) 110 advantageously stopor limit the seams 112 from extending completely through the multi-layersealing films 102. By stopping or limiting the seams 112, themulti-layer sealing films 102 advantageously prevent or limit thelikelihood of the ambient pressure P_(a) equalizing with the referencepressure P_(r) through the vent openings 106. Accordingly, yield may behigh during bulk manufacture of the MEMS package, and the reliability ofthe multi-layer sealing films 102 may be high.

With reference to FIG. 4B, a top view 400B of some embodiments of theMEMS package of FIG. 4A is provided. The top view 400B may, for example,be taken along line B-B′ in FIG. 4A. As illustrated, the channels 410 cof the cavity 410 are on opposite sides of the cavity 410 and havechannel widths W_(c) that are less than a bulk width W_(b) of the cavity410. Further, in some embodiments, the channels 410 c are at awidth-wise center of the cavity 410.

With reference to FIG. 4C, an exploded perspective view 400C of the MEMSpackage of FIG. 4A is provided. FIG. 4C is “exploded” in that the MEMSsubstrate 404 is separated from the support structure 402 on which theMEMS substrate 404 normally rests. The exploded perspective view 400Cmay, for example, be taken along line C-C′ in FIG. 4B.

While FIGS. 4A-4C illustrate the multi-layer sealing films 102 accordingto the embodiments of FIG. 1A, it is to be understood that themulti-layer sealing films 102 may be according to the embodiments ofFIG. 1B in other embodiments. Further, the multi-layer sealing films 102may have more or less metal layers in other embodiments, and/or more orless barrier layers in other embodiments. Also, while FIGS. 4A-4Cillustrate the MEMS package with two vent openings, two channel pads,and two channels, it is to be understood that the MEMS package may havemore or less vent openings, more or less channel pads, and more or lesschannels in other embodiments.

With reference to FIG. 5, a cross-sectional view 500 of some moredetailed embodiments of the MEMS package of FIGS. 4A-4C is provided. Asillustrated, the support structure 402 comprises a semiconductorsubstrate 502, a plurality of semiconductor devices 504, and aninterconnect structure 506. For ease of illustration, only some of thesemiconductor devices 504 are labeled 504. The semiconductor devices 504are over the semiconductor substrate 502, recessed into a top of thesemiconductor substrate 502. The semiconductor devices 504 may be, forexample, insulated-gate field-effect transistors (IGFETs), complementarymetal-oxide-semiconductor (CMOS) devices, or some other type ofsemiconductor device. The semiconductor substrate 502 may be, forexample, a bulk substrate of monocrystalline silicon or some other typeof semiconductor substrate.

The interconnect structure 506 covers the semiconductor devices 504 andthe semiconductor substrate 502, and electrically couples thesemiconductor devices 504 to one another and/or to the MEMS device 408.The interconnect structure 506 comprises an interconnect dielectriclayer 508, as well as a plurality of wires 510, a plurality of vias 512,and the channel pads 412 c. For ease of illustration, only some of thewires 510 are labeled 510, and only some of the vias 512 are labeled512. The interconnect dielectric layer 508 may be, for example, silicondioxide, silicon nitride, a low κ dielectric, some other dielectric, ora combination of the foregoing. As used herein, a low κ dielectric is adielectric with a dielectric constant κ less than about 3.9, 3.0, 2.0,or 1.0

The wires 510, the vias 512, and the channel pads 412 c are stacked inthe interconnect dielectric layer 508, and define conductive pathsbetween the semiconductor devices 504 and the MEMS device 408. In someembodiments, the wires 510 are alternatingly stacked with the vias 512,and/or the channel pads 412 c are at the top of the interconnectstructure 506. In some embodiments, some or all of the vias 512 eachextend vertically from one of the wires 510 to another one of the wires510, one of the channel pads 412 c, or one of the semiconductor devices504. In some embodiments, some or all of the wires 510 each extendlaterally from one of the vias 512 to another one of the vias 512. Thewires 510, the vias 512, and the channel pads 412 c are conductive andmay be, for example, aluminum copper, copper, aluminum, tungsten, someother conductive material, or a combination of the foregoing.

The MEMS substrate 404 is over the interconnect structure 506, and isbonded to the interconnect structure 506 at the bond interface 406. Insome embodiments, the bond interface 406 is between the MEMS substrate404 and the interconnect dielectric layer 508. The MEMS substrate 404comprises the MEMS device 408. The MEMS device 408 is spaced over theinterconnect structure 506 by the cavity 410 and is electrically coupledto the semiconductor devices 504 by the interconnect structure 506. Notethat electrical paths between the semiconductor devices 504 and the MEMSdevice 408 are not fully shown. The cavity 410 is hermetically sealedand, in some embodiments, is recessed into the interconnect dielectriclayer 508. Further, the MEMS substrate 404 comprises the vent openings106 on opposite sides of the cavity 410, which are respectively coveredby the multi-layer sealing films 102.

Seams 112 may form at the vent openings 106, along grain boundaries ofthe metal layers 108 of the multi-layer sealing films 102. The barrierlayers 110 advantageously stop or limit the seams 112 from extendingcompletely through the multi-layer sealing films 102. By stopping orlimiting the seams 112, the multi-layer sealing films 102 advantageouslyprevent or limit the likelihood of the pressure in the cavity 410equalizing with an ambient pressure of the MEMS package through the ventopenings 106. Accordingly, yield may be high (e.g., greater than 99%)during bulk manufacture of the MEMS package, and the reliability of themulti-layer sealing films 102 may be high. Further, the multi-layersealing films 102 may have a small thickness, thereby leading to lowmaterial costs.

With reference to FIG. 6A, a cross-sectional view 600A of some moredetailed embodiments of the MEMS package of FIG. 5 is provided. Asillustrated, the support structure 402 comprises the semiconductorsubstrate 502, the plurality of semiconductor devices 504, and theinterconnect structure 506. For ease of illustration, only some of thesemiconductor devices 504 are labeled 504. The semiconductor devices 504are recessed into a top of the semiconductor substrate 502, and theinterconnect structure 506 covers the semiconductor devices 504 and thesemiconductor substrate 502.

The interconnect structure 506 comprises a first interconnect dielectriclayer 508 a and a second interconnect dielectric layer 508 b, as well asthe plurality of wires 510, the plurality of vias 512, and a pluralityof pads 412. For ease of illustration, only some of the wires 510 arelabeled 510, only some of the vias 512 are labeled 512, and only some ofthe pads 412 are labeled 412. The second interconnect dielectric layer508 b covers the first interconnect dielectric layer 508 a. Further, thefirst interconnect dielectric layer 508 a and the second interconnectdielectric layer 508 b may be, for example, silicon dioxide, siliconnitride, a low κ dielectric, some other dielectric, or a combination ofthe foregoing.

The wires 510, the vias 512, and the pads 412 are stacked in the firstand second interconnect dielectric layers 508 a, 508 b. In someembodiments, the wires 510 are alternatingly stacked with the vias 512,and/or the pads 412 are at the top of the interconnect structure 506.Further, in some embodiments, one or more of the pads 412 are exposed byone or more respective pad openings 602 in the second interconnectdielectric layer 508 b. The wires 510, the vias 512, and the pads 412are conductive and may be, for example, aluminum copper, copper,aluminum, tungsten, some other conductive material, or a combination ofthe foregoing.

In some embodiments, the interconnect structure 506 further comprises anoutgas sing prevention layer 604 between the first and secondinterconnect dielectric layers 508 a, 508 b. The outgassing preventionlayer 604 may, for example, prevent gases from outgassing thereunder tothe cavity 410 overlying the outgassing prevention layer 604. Theoutgassing prevention layer 604 may, for example, have a gaspermissibility lower than that of the first interconnect dielectriclayer 508 a. Further, the outgassing prevention layer 604 may, forexample, be employed as an etch stop layer during formation of thecavity 410. In some embodiments, the outgas sing prevention layer 604 issilicon nitride, silicon oxynitride, silicon carbide, siliconoxycarbide, silicon carbon nitride, or a combination the foregoing.

The MEMS substrate 404 is over the interconnect structure 506, and isbonded to the interconnect structure 506 at the bond interface 406. TheMEMS substrate 404 comprises the MEMS device 408 and the vent openings106. The MEMS device 408 is spaced over the interconnect structure 506by the cavity 410 and is electrically coupled to the semiconductordevices 504 by the interconnect structure 506. The vent openings 106extend through the MEMS substrate 404, from the upper side 404 u of theMEMS substrate 404 to the cavity 410. In some embodiments, the ventopenings 106 overlie respective ones of the pads 412 in the cavity 410.

The multi-layer sealing films 102 cover the vent openings 106, and sealthe vent openings 106 and the caity 410, so a pressure in the cavity 410does not equalize with an ambient pressure of the MEMS package throughthe vent openings 106. The multi-layer sealing films 102 are eachconfigured as shown in FIG. 1A or 1B, and each include a plurality ofmetal layers (not shown) and one or more barrier layers (not shown)alternatingly stacked with the metal layers. As discussed above, thebarrier layer(s) advantageously stop seems that may develop at the ventopenings 106 from extending through the multi-layer sealing films 102and breaking the seal of the vent openings 106 and the cavity 410.

In some embodiments, one or more gas getter structures 606 are in thecavity 410. The gas getter structure(s) 606 are configured to absorbgases within the cavity 410. The gas getter structure 606 are orcomprise, for example, barium, aluminum, magnesium, calcium, sodium,strontium, cesium, phosphorus, platinum, titanium, some other gettermaterial, or a combination of the foregoing.

In some embodiments, a trench 608 and/or a plurality of via openings 610extend(s) vertically into the MEMS substrate 404 and the secondinterconnect dielectric layer 508 b. In some embodiments, the trench 608and/or the via openings 610 each have a width W that discretely tapersat the bond interface 406 between the MEMS substrate 404 and the secondinterconnect dielectric layer 508 b. Further, in some embodiments, thetrench and/or the via openings 610 each extend to and stop on arespective one of the pads 412. The trench 608 comprises a pair ofsegments (not labeled) respectively on opposite sides of the cavity 410and, in some embodiments, the via openings 610 are spaced between thesegments.

In some embodiments, a plurality of through substrate vias (TSVs) 612are respectively in the via openings 610. In some embodiments, the TSVs612 conformally line the via openings 610 so as to only partially fillthe via openings 610. Further, in some embodiments, the TSVs 612electrically couple the MEMS device 408 to the interconnect structure506. The TSVs 612 may, for example, have the same structure as themulti-layer sealing films 102. That is to say, the TSVs 612 may, forexample, comprise a plurality of metal layers and one or more barrierlayers alternatingly stacked with the metal layers. Examples of suchalternating stacking are shown in FIGS. 1A and 1B with regard to themulti-layer sealing film 102. Further, the TSVs 612 may, for example,comprise copper, aluminum, aluminum copper, titanium nitride, tantalumnitride, some other conductive material, or a combination of theforegoing.

In some embodiments, a passivation layer 614 covers and conformallylines the trench 608 and/or the TSVs 612. The passivation layer 614prevents gases and/or moisture from diffusing from the ambientenvironment of the MEMS package to the cavity 410, and vice versa. Insome embodiments, the passivation layer 614 is silicon nitride, silicondioxide, silicon oxynitride, or some other dielectric layer.

With reference to FIG. 6B, a top view 600B of some embodiments of theMEMS package of FIG. 6A is provided. The top view 600B may, for example,be taken along line D-D′ in FIG. 6A. As illustrated, the trench 608extends laterally to completely enclose the cavity 410 and, in someembodiments, the TSVs 612. Further, in some embodiments, the trench 608conforms to the cavity 410 while remaining spaced from the cavity 410.Further yet, in some embodiments, the via openings 610 have, forexample, a square layout, a rectangular layout, a triangular layout, acircular layout, or some other layout.

With reference to FIG. 6C, an enlarged, partial cross-sectional view600C of the MEMS package of FIG. 6A is provided. The enlarged, partialcross-sectional view 600C may, for example, correspond to circle E inFIG. 6A or circle E′ in FIG. 6A. As illustrated, the multi-layer sealingfilms 102 each comprise a plurality of metal layers 108 and one or morebarrier layers 110. The metal layers 108 and the barrier layer(s) 110are alternatingly stacked, examples of which are shown in FIGS. 1A and1B. Further, the metal layers 108 are metals with grain sizes largerthan those of the barrier layer(s) 110, and the barrier layer(s) 110 aremetals or ceramics with grain sizes smaller than those of the metallayers 108.

With reference to FIGS. 7-11, 12A, 12B, 13A, and 13B, a series ofcross-sectional views 700-1100, 1200A, 1200B, 1300A, 1300B of someembodiments of a method for manufacturing a MEMS package with amulti-layer sealing film is provided. Such embodiments may, for example,be employed to manufacture the MEMS package of FIG. 5.

As illustrated by the cross-sectional view 700 of FIG. 7, a supportstructure 402 is provided or otherwise formed. The support structure 402is an IC and comprises a semiconductor substrate 502, a plurality ofsemiconductor devices 504, and an interconnect structure 506. For easeof illustration, only some of the semiconductor devices 504 are labeled504. The semiconductor devices 504 are recessed into a top of thesemiconductor substrate 502, and the interconnect structure 506 coversthe semiconductor substrate 502 and the semiconductor devices 504. Thesemiconductor devices 504 may be or include, for example, CMOS devicesor other types of semiconductor devices. The interconnect structure 506comprises an interconnect dielectric layer 508, and further compriseswires 510, vias 512, and a pair of channel pads 412 c stacked in in theinterconnect dielectric layer 508. For ease of illustration, only someof the wires 510 are labeled 510, and only some of the vias 512 arelabeled 512. In some embodiments, the channel pads 412 c are at a top ofthe interconnect dielectric layer 508.

As illustrated by the cross-sectional view 800 of FIG. 8, a first etchis performed into the interconnect dielectric layer 508 to form a cavity410 in the interconnect dielectric layer 508. An example layout of thecavity 410 is illustrated in FIG. 4B. The cavity 410 is formed with apair of channels 410 c on opposite sides of the cavity 410. The channels410 c are laterally elongated and have a channel depth D_(c) that isless than a bulk depth D_(b) of the cavity 410. The channels 410 cfurther respectively overlie the channel pads 412 c.

In some embodiments, a process for performing the first etch comprisesforming a patterned photoresist layer 802 on the interconnect dielectriclayer 508. The patterned photoresist layer 802 is formed with an openingcorresponding to the cavity 410 and may, for example, be patterned withphotolithography. Further, in some embodiments, the process comprisesapplying an etchant 804 to the interconnect dielectric layer 508 withthe patterned photoresist layer 802 in place, and subsequently strippingthe patterned photoresist layer 802 from the interconnect dielectriclayer 508. In some embodiments, the channel pads 412 c serve as etchstops during the first etch.

As illustrated by the cross-sectional view 900 of FIG. 9, a MEMSsubstrate 404 is arranged over and bonded to the support structure 402at a bond interface 406. In some embodiments, the bond interface 406 isformed by fusion bonding and/or the bond interface 406 is a location atwhich a bottom surface of the MEMS substrate 404 interfaces with a topsurface of the interconnect dielectric layer 508. Further, in someembodiments, the bonding hermetically seals the cavity 410. The cavity410 may, for example, be hermetically sealed with a high referencepressure. The high reference pressure may, for example, be a pressuregreater than about 500, 750, or 1100 millibars, and/or may, for example,be between about 500-1100, 500-750, 750-100, or 250-750 millibars.Further, after the bonding, the high reference pressure may, forexample, be different than an ambient pressure of the MEMS package thatis at the upper side 404 u of the MEMS substrate 404. The MEMS substrate404 may be or comprise, for example, monocrystalline silicon,polycrystalline silicon, amorphous silicon, aluminum copper, oxide,silicon nitride, or a combination of the foregoing.

As illustrated by the cross-sectional view 1000 of FIG. 10, in someembodiments, the MEMS substrate 404 is thinned to a thickness T_(s). Thethickness T_(s) may, for example, be between about 0.1-40.0 micrometers,about 0.1-10 micrometers, about 10-30 micrometers, about 15-25micrometers, about 5-15 micrometers, or about 25-35 micrometers. Thethinning may, for example, be performed by chemical mechanical polishing(CMP).

Also illustrated by the cross-sectional view 1000 of FIG. 10, the MEMSsubstrate 404 comprises a MEMS device 408 overlying the cavity 410. TheMEMS device 408 may be, for example, a pressure sensor, and/or may, forexample, move within the cavity 410 based on a pressure differencebetween the cavity 410 and an upper side 404 u of the MEMS substrate404. In some embodiments, the MEMS device 408 is formed in the MEMSsubstrate 404 before the MEMS substrate 404 is bonded to the supportstructure 402 at FIG. 9. In other embodiments, the MEMS device 408 isformed in the MEMS substrate 404 after the MEMS substrate 404 is thinnedto the thickness T_(s) at FIG. 10. In yet other embodiments, the MEMSdevice 408 is formed in the MEMS substrate 404 between the bonding andthe thinning.

As illustrated by the cross-sectional view 1100 of FIG. 11, a secondetch is performed into the MEMS substrate 404 to form a pair of ventopenings 106 extending through MEMS substrate 404, from the upper side404 u of the MEMS substrate 404 to the cavity 410. In some embodiments,the second etch breaks a hermetic seal of the cavity 410 to equalize apressure in the cavity 410 with a pressure on the upper side 404 u ofthe MEMS substrate 404. The vent openings 106 may, for example, be onopposite sides of the cavity 410, and/or may, for example, respectivelyoverlie the channels 410 c of the cavity 410. Further, the vent openings106 may, for example, have a rectangular, a triangular, a circular, anoval-shaped, a hexagonal-shaped, a square-shaped layout, or some otherlayout. In some embodiments, t the vent openings 106 each have a layoutas shown in FIG. 2A or FIG. 2B.

Minimum dimensions D individual to the vent openings 106 may, forexample, each be between about 0.1-2.0 micrometers, about 0.05-5.0micrometers, about 0.5-1.5 micrometers, about 1.0-1.5 micrometers, orabout 0.1-1.0 micrometers. Further yet, the minimum dimensions D of thevent openings 106 may, for example, be greater than or equal to about1/20^(th) of the thickness T_(s) of the MEMS substrate 404 or about1/30^(th) of the thickness T_(s) of the MEMS substrate 404, and/or may,for example, be between about 1/15^(th)- 1/25^(th) of the thicknessT_(s) of the MEMS substrate 404, about 1/18^(th)- 1/22^(th) of thethickness T_(s) of the MEMS substrate 404, or about 1/10^(th)- 1/30^(th)of the thickness T_(s) of the MEMS substrate 404.

In some embodiments, a process for performing the second etch comprisesforming a patterned photoresist layer 1102 on the MEMS substrate 404.The patterned photoresist layer 1102 is formed with a pattern ofopenings corresponding to the vent openings 106 and may, for example, bepatterned with photolithography. Further, in some embodiments, theprocess comprises applying an etchant 1104 to the MEMS substrate 404with the patterned photoresist layer 1102 in place to transfer thepattern of openings to the MEMS substrate 404. Further yet, in someembodiments, the process comprises stripping the patterned photoresistlayer 1102 from the MEMS substrate 404 after the second etch.

As illustrated by the cross-sectional view 1200A of FIG. 12A, amulti-layer sealing film 102′ is formed covering the MEMS substrate 404and the vent openings 106, and further sealing the vent openings 106 andthe cavity 410. In some embodiments, the vent openings 106 and thecavity 410 are sealed with a low pressure. The low pressure may, forexample, be less than about 10, 100, 250, or 500 millibars, and/or lessthan a pressure at which the bonding at FIG. 7 is performed. Further,the low pressure may, for example, be between about 0.001-10.000millibar, about 10-500 millibar, about 0.001-1.000 millibar, or about10-100 millibar. The multi-layer sealing film 102′ comprises a firstmetal layer 108 a′, a first barrier layer 110 a′, a second metal layer108 b′, a second barrier layer 110 b′, and a third metal layer 108 c′.

The first metal layer 108 a′ is over the MEMS substrate 404. The firstbarrier layer 110 a′ is over the first metal layer 108 a′. The secondmetal layer 108 b′ is over the first barrier layer 110 a′. The secondbarrier layer 110 b′ is over the second metal layer 108 b′. The thirdmetal layer 108 c′ is over the second barrier layer 110 b′. The first,second, and third metal layers 108 a′-108 c′ are metals with grain sizeslarger than those of the first and second barrier layers 110 a′, 110 b′,and the first and second barrier layers 110 a′, 110 b′ are metals orceramics that have grain sizes smaller than those of the first, second,and third metal layers 108 a′-108 c′. For example, the first, second,and third metal layers 108 a′-108 c′ may be aluminum copper, copper, orsome other metal, and the first and second barrier layers 110 a′, 110 b′may be titanium nitride, titanium tungsten, tungsten nitride, tantalumnitride, or some other barrier layer.

In some embodiments, the first, second, and third metal layers 108a′-108 c′ each have a thickness T_(m) between about 0.5-1.5 micrometers,about 0.8-1.2 micrometers, or about 0.1-5 micrometers, and/or the firstand second barrier layers 110 a′, 110 b′ each have a thickness T_(b)between about 1100-2000 angstroms, about 1250-1750 angstroms, or about500-5000 angstroms. For example, the thickness T_(m) of the first,second, and third metal layers 108 a′-108 c′ may be about 1.0micrometers and the thickness T_(b) of the first and second barrierlayers 110 a′, 110 b′ may be about 1500 angstroms. In some embodiments,the first, second, and third metal layers 108 a′-108 c′ and the firstand second barrier layers 110 a′, 110 b′ have a combined thickness T_(f)greater than about half of the minimum dimensions D of the vent openings106, and/or between about 2.5-3.0 micrometers, about 2.7-3.3micrometers, or about 1.0-5.0 micrometers.

In some embodiments, a process for forming the multi-layer sealing film102′ comprising performing a series of growth and/or depositionprocesses to sequentially form the layers of the multi-layer sealingfilm 102′. The growth or deposition processes may include, for example,chemical vapor deposition (CVD), physical vapor deposition (PVD),electron beam PVD, electroplating, electroless plating, some othergrowth or deposition process, or a combination of the foregoing.Further, the growth and/or deposition processes may, for example, beperformed at the low pressure at which the cavity 410 is to be sealed.

Advantageously, re-sealing the vent openings 106 and the cavity 410 withthe multi-layer sealing films 102 may allow the vent openings 106 andthe cavity 410 to have the low pressure. Namely, where the bonding atFIG. 9 is performed by fusion bonding, the cavity 410 may be limited toan initial pressure that is high since fusion bonding is performed athigh pressures. Such high pressures may, for example, be greater thanabout 500, 600, 750, or 1100 millibars. Further, since the multi-layersealing film 102′ may be formed at the low pressure, the re-sealingallows the vent openings 106 and the cavity 410 to have the lowpressure.

As illustrated by the cross-sectional view 1200B of FIG. 12B, in someembodiments, a third etch is performed into the multi-layer sealing film102′ (see FIG. 12A) to form a pair of individual multi-layer sealingfilms 102 respectively covering the vent openings 106, and furthersealing the vent openings 106 and the cavity 410. The individualmulti-layer sealing films 102 each comprise a plurality of individualmetal layers 108 and a plurality of individual barrier layers 110alternatingly stacked with the individual metal layers 108. For ease ofillustration, only some of the individual metal layers 108 are labeled108, and only some of the individual barrier layers 110 are labeled 110.

In some embodiments, a process for performing the third etch comprisesforming a patterned photoresist layer 1202 on the multi-layer sealingfilm 102. The patterned photoresist layer 1202 is formed with a patternof openings corresponding to gaps between the individual multi-layersealing films 102 and may, for example, be patterned withphotolithography. Further, in some embodiments, the process comprisesapplying an etchant 1204 to the multi-layer sealing film 102′ with thepatterned photoresist layer 1202 in place to transfer the pattern ofopenings to the multi-layer sealing film 102′. Further yet, in someembodiments, the process comprises stripping the patterned photoresistlayer 1202 after the third etch.

As discussed above, after the individual multi-layer sealing films 102are formed, seams may form at the vent openings 106. The individualbarrier layers 110 advantageously stop or limit the seams from extendingcompletely through the individual multi-layer sealing films 102 andbreaking the seals. Accordingly, yield may be high during bulkmanufacture of the MEMS package, and the reliability of the individualmulti-layer sealing films 102 may be high. Further, material costs maybe low since a thickness of the individual multi-layer sealing films 102may be small while still achieve a high yield.

While FIGS. 12A and 12B illustrate the formation of individualmulti-layer sealing films 102 with three metal layers and two barrierlayers, the individual multi-layer sealing films 102 may be formed withmore or less metal and barrier layers in other embodiments. For example,FIGS. 13A and 13B illustrate the formation of the individual multi-layersealing films 102 with two metal layers and one barrier layer.

As illustrated by the cross-sectional view 1300A of FIG. 13A, themulti-layer sealing film 102′ is formed with the first metal layer 108a′, the first barrier layer 110 a′, and the second metal layer 108 b′,but not the second barrier layer 110 b′ (see FIG. 12A) and the thirdmetal layer 108 c′ (see FIG. 12A). Further, the thickness T_(m) of thefirst and second metal layers 108 a′, 108 b′ may be, for example, about1.25-1.75 micrometers, such as 1.5 micrometers, and the thickness T_(b)of the first barrier layer 110 a′ may be about 1500 angstroms.

As illustrated by the cross-sectional view 1300B of FIG. 13B, in someembodiments, the individual multi-layer sealing films 102 are formedrespectively covering the vent openings 106, and further sealing thevent openings 106 and the cavity 410. Further, the individualmulti-layer sealing films 102 each comprise a plurality of individualmetal layers 108 and a single individual barrier layer 110 alternatinglystacked with the individual metal layers 108. For ease of illustration,only some of the individual metal layers 108 are labeled 108.

With reference to FIG. 14, a flowchart 1400 of some embodiments of themethod of FIGS. 7-11, 12A, 12B, 13A, and 13B is provided.

At 1402, a support structure is provided. See, for example, FIG. 7.

At 1404, a first etch is performed into a top of the support structureto form a cavity in the support structure. See, for example, FIG. 8.

At 1406, a MEMS substrate is bonded to the top of the support structureto hermetically seal the cavity between the support structure and theMEMS substrate. See, for example, FIG. 9.

At 1408, the MEMS substrate is thinned to a target thickness. See, forexample, FIG. 10.

At 1410, a second etch is performed into a top of the MEMS substrate toform a vent opening extending through the MEMS substrate to the cavity.See, for example, FIG. 11.

At 1412, a multi-layer sealing film is formed covering the MEMSsubstrate and the vent opening, and further hermetically sealing thevent opening and the cavity. The multi-layer sealing film comprises apair of metal layers and a barrier layer sandwiched between the metallayers. See, for example, FIG. 12A or FIG. 13A. The barrier layeradvantageously stops or limits a seam from extending through themulti-layer sealing film, from the vent opening, and breaking the sealof the multi-layer sealing film.

At 1414, a third etch is performed into the multi-layer sealing film topattern the multi-layer sealing film. See, for example, FIG. 12B or FIG.13B)

While the flowchart 1400 of FIG. 14 is illustrated and described hereinas a series of acts or events, it will be appreciated that theillustrated ordering of such acts or events is not to be interpreted ina limiting sense. For example, some acts may occur in different ordersand/or concurrently with other acts or events apart from thoseillustrated and/or described herein. Further, not all illustrated actsmay be required to implement one or more aspects or embodiments of thedescription herein, and one or more of the acts depicted herein may becarried out in one or more separate acts and/or phases.

In view of the foregoing, some embodiments of the present applicationprovide a MEMS package including a support structure, a MEMS substrate,and a multi-layer sealing film. The MEMS substrate is over and bonded tothe support structure. The support structure and the MEMS substratedefine a cavity between the support structure and the MEMS substrate.The MEMS substrate includes a vent opening extending through the MEMSsubstrate, from an upper side of the MEMS substrate to the cavity. Themulti-layer sealing film covers and seals the vent opening to prevent afirst pressure on the upper side of the MEMS substrate from equalizingwith a second pressure in the cavity through the vent opening. Themulti-layer sealing film includes a pair of metal layers and a barrierlayer sandwiched between metal layers. In an embodiment, the barrierlayer is conductive and includes a metal or a ceramic, and the metal orthe ceramic has a grain size less than a grain size of the metal layers.In an embodiment, the metal layers includes aluminum or copper, and thebarrier layer includes titanium or tantalum. In an embodiment, the pairof metal layers includes a first metal layer and a second metal layer;the barrier layer overlies and contacts the first metal layer; and thesecond metal layer overlies and contacts the barrier layer. In anembodiment, the MEMS package further includes a second barrier layeroverlying and contacting the second metal layer; and a third metal layeroverlying and contacting the second barrier layer. In an embodiment, thefirst metal layer includes a seam extending from the vent opening, alonggrain boundaries of the first metal layer, to the barrier layer, and theseam terminates at the barrier layer. In an embodiment, the cavityincludes a channel; the channel extends laterally away from a bulk ofthe cavity in a first direction and along a length of the channel; thechannel has a smaller width and a smaller depth than the bulk of thecavity; the vent opening overlies the channel, and the vent opening andthe bulk of the cavity are on opposite sides of the channel. In anembodiment, the cavity includes a second channel; the second channelextends laterally away from the bulk of the cavity in a second directionand along a length of the second channel; the second direction isopposite the first direction; the second channel has a smaller width anda smaller depth than the bulk of the cavity; the MEMS substrate includesa second vent opening overlying the second channel; and the second ventopening and the bulk of the cavity are on opposite sides of the secondchannel. In an embodiment, the MEMS package further includes aconductive pad underlying the channel and defining a bottom surface ofthe channel. In an embodiment, the support structure includes asemiconductor substrate and an interconnect structure covering thesemiconductor substrate; the interconnect structure includes aninterconnect dielectric layer, vias, and wires; and the vias and thewires are alternatingly stacked in the interconnect dielectric layer.

Some embodiments of the present application provide a method formanufacturing a MEMS package. A first etch is performed into a supportstructure to form a cavity in the support structure. A MEMS substrate isbonded to the support structure to seal the cavity. A second etch isperformed into the MEMS substrate to form a vent opening unsealing thecavity. A multi-layer sealing film is formed covering the vent opening,and further sealing the vent opening and the cavity. The multi-layersealing film includes a pair of metal layers and a barrier layersandwiched between metal layers. In an embodiment, the barrier layer isformed of a metal or ceramic with smaller grains that those of the metallayers. In an embodiment, the bonding hermetically seals the cavity witha first pressure; and the forming of the multi-layer sealing film sealsthe cavity with a second pressure different than the first pressure. Inan embodiment, the second pressure is low compared to the firstpressure. In an embodiment, the bonding is performed by fusion bonding abottom surface of the MEMS substrate to a top surface of the supportstructure. In an embodiment, the support structure includes asemiconductor substrate and an interconnect structure; the interconnectstructure covers the semiconductor substrate; the interconnect structureincludes an interconnect dielectric layer, wires, vias, and pads; thewires, the vias, and the pads are stacked in the interconnect dielectriclayer; and the first etch is performed directly into the interconnectdielectric layer. In an embodiment, the pads are at a top of theinterconnect structure and include a pair of channel pads; the channelpads are laterally spaced; the first etch is performed into theinterconnect dielectric layer to form the cavity between the channelpads and overlapping the channel pads; and the channel pads serve as anetch stop for the first etch. In an embodiment, the pair of metal layersinclude a first metal layer and a second metal layer; and the forming ofthe multi-layer sealing film includes forming the first metal layercovering the vent opening and the MEMS substrate, forming the barrierlayer overlying and covering the first metal layer, and forming thesecond metal layer overlying and covering the barrier layer. In anembodiment, the forming of the multi-layer sealing film includes forminga second barrier layer overlying and covering the second metal layer;and forming a third metal layer overlying and covering the secondbarrier layer.

Some embodiments of the present application provide another MEMS packageincluding a support structure, a MEMS substrate, and a pair ofmulti-layer sealing films. The support structure includes asemiconductor substrate and an interconnect structure. The interconnectstructure covers the semiconductor substrate. The interconnect structureincludes a dielectric layer, vias, wires, and a pair of channel pads.The vias, the wires, and the channel pads are stacked in the dielectriclayer. The MEMS substrate is over and bonded to the interconnectstructure. The interconnect structure and the MEMS substrate define acavity laterally between the channel pads and vertically between theinterconnect structure and the MEMS substrate. The MEMS substrateincludes a MEMS device and a pair of vent openings. The vent openingsextend through the MEMS substrate, from a top of the MEMS substrate tothe cavity, and respectively overlie the channel pads. The channel padsare in the cavity. The multi-layer sealing films respectively cover andseal the vent openings to prevent a first pressure at the top of theMEMS substrate from equalizing with a second pressure in the cavitythrough the vent openings. The multi-layer sealing films each include apair of metal layers and a barrier layer sandwiched between metallayers. The metal layers have larger metal grains than the barrierlayer.

Some embodiments of the present application provide a semiconductorstructure including a substrate and a multi-layer sealing film. Thesubstrate includes a vent opening extending through the substrate, froman upper side of the substrate to a lower side of the substrate. Theupper side of the substrate has a first pressure, and the lower side ofthe substrate has a second pressure different than the first pressure.The multi-layer sealing film covers and seals the vent opening toprevent the first pressure from equalizing with the second pressurethrough the vent opening. The multi-layer sealing film includes a pairof metal layers and a barrier layer sandwiched between metal layers. Inan embodiment, the multi-layer sealing film further includes anadditional barrier layer and an additional metal layer; the additionalbarrier layer overlies the metal layers and the barrier layer; and theadditional metal layer overlies the additional barrier layer. In anembodiment, the barrier layer is metal or ceramic and has a grain sizeless than a grain size of the metal layers.

Some embodiments of the present application provide a method formanufacturing a semiconductor structure. A substrate is provided. Thesubstrate has a first pressure on a lower side of the substrate and asecond pressure on an upper side of the substrate. The lower and uppersides of the substrate are opposite, and the first and second pressuresare different. A etch is performed into the substrate to form ventopening extending through the substrate, from the upper side of thesubstrate to the lower side of the substrate, and to further equalizethe first and second pressures through the vent opening. A multi-layersealing film is formed covering and sealing the vent opening. Themulti-layer sealing film is formed at a third pressure different thanthe first pressure. The multi-layer sealing film includes a pair ofmetal layers and a barrier layer sandwiched between metal layers. In anembodiment, the barrier layer is formed of a metal or ceramic withsmaller grains that those of the metal layers. In an embodiment, themetal layers are formed of aluminum or copper; and the barrier layer isformed of titanium or tantalum. In an embodiment, the forming of themulti-layer sealing film further includes forming an additional barrierlayer overlying and covering the metal layers; and forming an additionalmetal layer overlying and covering the additional barrier layer.

Some embodiments of the present application provide another method formanufacturing a MEMS package. A support structure is provided. Thesupport structure includes a semiconductor substrate, semiconductordevices recessed into a top of the semiconductor substrate, and aninterconnect structure covering the semiconductor substrate and thesemiconductor devices. The interconnect structure includes a dielectriclayer and conductive features stacked in the dielectric layer. A firstetch is performed into a top of the dielectric layer to form a cavity inthe dielectric layer. The cavity has a T-shaped profile. A MEMSsubstrate is fusion bonded to the top of the dielectric layer tohermetically seal the cavity. The cavity is hermetically sealed with afirst pressure. A second etch is performed into a top of the MEMSsubstrate to form a pair of vent openings unsealing the cavity. The ventopenings are on opposite sides of the cavity. A multi-layer sealing filmis formed covering and sealing the vent openings and the cavity. Themulti-layer sealing film seals the vent openings and the cavity with asecond pressure different than the first pressure. The multi-layersealing film includes a pair of metal layers and a barrier layersandwiched between metal layers. In an embodiment, the conductivefeatures include a pair of channel pads at a top of the interconnectstructure; the first etch is performed into the dielectric layer to formthe cavity between the channel pads and overlapping the channel pads;and the channel pads serve as an etch stop for the first etch. In anembodiment, the multi-layer sealing film is formed at the secondpressure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for manufacturing amicroelectromechanical systems (MEMS) package, the method comprising:performing a first etch into a support structure to form a cavity in thesupport structure; bonding a MEMS substrate to the support structure toseal the cavity; performing a second etch into the MEMS substrate toform a vent opening unsealing the cavity; and forming a multi-layersealing film covering the vent opening, and further sealing the ventopening and the cavity, wherein the multi-layer sealing film comprises apair of metal layers and a conductive barrier layer sandwiched betweenand directly contacting the metal layers.
 2. The method according toclaim 1, wherein the conductive barrier layer is formed of a metal orceramic with smaller grains that those of the metal layers.
 3. Themethod according to claim 1, wherein the bonding hermetically seals thecavity with a first pressure, and wherein the forming of the multi-layersealing film seals the cavity with a second pressure different than thefirst pressure.
 4. The method according to claim 3, wherein the secondpressure is low compared to the first pressure.
 5. The method accordingto claim 1, wherein the conductive barrier layer is sandwiched betweenthe metal layers along a vertical axis and directly contacts the metallayers along the vertical axis.
 6. The method according to claim 1,wherein the support structure comprises a semiconductor substrate and aninterconnect structure, wherein the interconnect structure covers thesemiconductor substrate, wherein the interconnect structure comprises aninterconnect dielectric layer, wires, vias, and pads, wherein the wires,the vias, and the pads are stacked in the interconnect dielectric layer,and wherein the first etch is performed directly into the interconnectdielectric layer.
 7. The method according to claim 6, wherein the padsare at a top of the interconnect structure and comprise a pair ofchannel pads, wherein the channel pads are laterally spaced, wherein thefirst etch is performed into the interconnect dielectric layer to formthe cavity between the channel pads and overlapping the channel pads,and wherein the channel pads serve as an etch stop for the first etch.8. The method according to claim 1, wherein the pair of metal layerscomprises a first metal layer and a second metal layer, and wherein theforming of the multi-layer sealing film comprises: forming the firstmetal layer covering the vent opening and the MEMS substrate; formingthe conductive barrier layer overlying and covering the first metallayer; and forming the second metal layer overlying and covering theconductive barrier layer.
 9. The method according to claim 8, whereinthe forming of the multi-layer sealing film comprises: forming a secondconductive barrier layer overlying and covering the second metal layer;and forming a third metal layer overlying and covering the secondconductive barrier layer.
 10. A method for forming amicroelectromechanical systems (MEMS) package, the method comprising:forming an interconnect dielectric structure on a substrate and aplurality of wires and a plurality of vias stacked in the interconnectdielectric structure; patterning the interconnect dielectric structureto form a cavity in the interconnect dielectric structure; bonding aMEMS substrate to the interconnect dielectric structure to seal thecavity; patterning the MEMS substrate to form a vent opening unsealingthe cavity; depositing a first metal layer on the MEMS substrate,wherein the first metal layer covers the vent opening and the MEMSsubstrate and is in direct fluid communication with an atmosphere of thecavity, and wherein the first metal layer further seals the vent openingand the cavity; depositing a first barrier layer on and covering thefirst metal layer; and depositing a second metal layer on and coveringthe first barrier layer.
 11. The method according to claim 10, whereinthe MEMS substrate is a bulk silicon substrate and directly contacts theinterconnect dielectric structure.
 12. The method according to claim 10,further comprising: forming a seam in the first metal layer, wherein theseam extends from the vent opening to the first barrier layer andterminates at the first barrier layer, and wherein the seam defines afluid path from the cavity to the first barrier layer.
 13. The methodaccording to claim 10, further comprising: depositing a second barrierlayer on and covering the second metal layer; and depositing a thirdmetal layer on and covering the second barrier layer.
 14. The methodaccording to claim 13, further comprising: forming a mask on the thirdmetal layer; and performing an etch into the first, second, and thirdmetal layers and the first and second barrier layers with the mask inplace to form a seal film covering and localized to the vent opening.15. The method according to claim 10, wherein the first barrier layer isconductive, and wherein the method further comprises: forming a maskdirectly on the second metal layer; and performing an etch into thefirst and second metal layers and the first barrier layer with the maskin place to form a sealing film covering and localized to the ventopening.
 16. A method for forming a microelectromechanical systems(MEMS) package, the method comprising: patterning a support structure toform a cavity in the support structure; bonding a MEMS substrate to thesupport structure to seal the cavity; patterning the MEMS substrate toform a vent opening unsealing the cavity; depositing a first conductivelayer covering the vent opening and the MEMS substrate, wherein thefirst conductive layer seals the vent opening and the cavity; depositinga barrier layer covering the first conductive layer and having firstcrystalline grains; and depositing a second conductive layer coveringthe barrier layer, wherein the first and second conductive layers havesecond and third crystalline grains, respectively, and wherein thesecond and third crystalline grains are larger in size than the firstcrystalline grains.
 17. The method according to claim 16, wherein thefirst and second conductive layers consist of a first set of one or moremetals, wherein the barrier layer consists of a second set of one ormore metals, and wherein the first and second sets are non-overlapping.18. The method according to claim 16, wherein the barrier layer isconductive and directly contacts the second conductive layer, andwherein the barrier layer has a bottommost surface that is above anuppermost surface of the MEMS substrate.
 19. The method according toclaim 16, further comprising: forming a mask on the second conductivelayer; and performing an etch into the first and second conductivelayers and the barrier layer with the mask in place.
 20. The methodaccording to claim 16, wherein the first conductive layer is formeddirectly contacting the MEMS substrate and in direct fluid communicationwith an atmosphere of the cavity.